linux-kernel - Re: [PATCH v2 5/5] mm/page_alloc.c: avoid allocating highmem pages via alloc_pages_exact[

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Message-ID: <1ef3dc5d-7eb9-90a5-afbf-f551afcf7d8b@redhat.com>
Date:   Thu, 2 Sep 2021 14:16:16 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     vbabka@...e.cz, sfr@...b.auug.org.au, peterz@...radead.org,
        mgorman@...hsingularity.net, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] mm/page_alloc.c: avoid allocating highmem pages
 via alloc_pages_exact[_nid]

On 02.09.21 14:12, Miaohe Lin wrote:
> Don't use with __GFP_HIGHMEM because page_address() cannot represent
> highmem pages without kmap(). Newly allocated pages would leak as
> page_address() will return NULL for highmem pages here. But It works
> now because the callers do not specify __GFP_HIGHMEM now.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>   mm/page_alloc.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9c09dcb24149..e1d0e27d005a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5614,8 +5614,8 @@ void *alloc_pages_exact(size_t size, gfp_t gfp_mask)
>   	unsigned int order = get_order(size);
>   	unsigned long addr;
>   
> -	if (WARN_ON_ONCE(gfp_mask & __GFP_COMP))
> -		gfp_mask &= ~__GFP_COMP;
> +	if (WARN_ON_ONCE(gfp_mask & (__GFP_COMP | __GFP_HIGHMEM)))
> +		gfp_mask &= ~(__GFP_COMP | __GFP_HIGHMEM);
>   
>   	addr = __get_free_pages(gfp_mask, order);
>   	return make_alloc_exact(addr, order, size);
> @@ -5639,8 +5639,8 @@ void * __meminit alloc_pages_exact_nid(int nid, size_t size, gfp_t gfp_mask)
>   	unsigned int order = get_order(size);
>   	struct page *p;
>   
> -	if (WARN_ON_ONCE(gfp_mask & __GFP_COMP))
> -		gfp_mask &= ~__GFP_COMP;
> +	if (WARN_ON_ONCE(gfp_mask & (__GFP_COMP | __GFP_HIGHMEM)))
> +		gfp_mask &= ~(__GFP_COMP | __GFP_HIGHMEM);
>   
>   	p = alloc_pages_node(nid, gfp_mask, order);
>   	if (!p)
> 

Ideally we would convert this WARN_ON_ONCE() to pr_warn_once(), but I 
guess this really never ever happens on a production system and would 
get caught early while testing.

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb